Electronic component including outermost layer of outer electrode not electrically connected to inner electrode and method for producing mount structure

This application claims the benefit of priority to Japanese Patent Application No. 2020-021662 filed on Feb. 12, 2020. The entire contents of this application are hereby incorporated herein by reference.

The present invention relates to an electronic component, a method for producing an electronic component, and a method for producing a mount structure.

Electronic components, such as multilayer ceramic capacitors, include a body, an inner electrode disposed within the body, and an outer electrode disposed outside of the body. As the method of mounting such an electronic component on a circuit board, the dominant method is to use solder to achieve bonding between a land of the circuit board and the outer electrode of the electronic component.

In this way, existing electronic components are to be soldered and, thus, are often provided with outer electrodes that have a trilayer structure. Japanese Unexamined Patent Application Publication No. 2000-357627 describes a trilayer outer electrode having the following structure: the first layer in contact with the body is formed by sintering metal; the second layer is a plated coating of Ni, Cu, or an alloy of the foregoing formed so as to cover the first layer; and the third layer is a plated coating of Sn or solder formed so as to cover the second layer.

The first layer of such an outer electrode is an underlying layer formed for establishing electrical connection to the inner electrode. However, when the first layer is brought into direct contact with solder for bonding to a land of the circuit board, the metal component of the first layer is absorbed by the solder, which is a phenomenon called “dissolution of metallization”. Thus, in order to prevent the dissolution of metallization phenomenon, the second layer defined by a plated coating of, for example, Ni is formed on the surface of the first layer. However, oxidation of the plated coating of the second layer results in a decrease in the adhesion to solder. Thus, in order to prevent oxidation of the plated coating of the second layer, the third layer defined by a plated coating of, for example, Sn is formed. As the third layer, use of the plated coating of, for example, Sn provides solder wettability.

As described above, the presence of an oxide film in the surface of the outer electrode causes a decrease in the adhesion to solder. Thus, solder ordinarily contains flux for removing oxide films.

However, the method of mounting an electronic component using soldering and plating may cause a reduction in the quality as described in (1) below. In particular, the method of mounting a ceramic electronic component including a body of ceramic may cause a reduction in the quality as described in, in addition to (1), (2) and (3) below.

Preferred embodiments of the present invention provide electronic components that are each mountable on a circuit board without soldering or plating, methods for producing such electronic components, and methods for producing mount structures using such electronic components.

An electronic component according to a preferred embodiment of the present invention includes a body, an inner electrode disposed within the body, and an outer electrode disposed outside of the body, wherein the outer electrode includes an outermost layer that includes metal particles but is not electrically connected to the inner electrode.

A method for producing an electronic component according to a preferred embodiment of the present invention includes a step of preparing a body within which an inner electrode is disposed, and a step of forming an outer electrode outside of the body, wherein, in the step of forming the outer electrode, an outermost-layer-forming conductive paste including metal particles and a solvent is applied to a surface, and subsequently, the outermost-layer-forming conductive paste is dried at a temperature at which the solvent evaporates but sintering of the metal particles does not begin, to form a dry film as an outermost layer of the outer electrode.

A method for producing a mount structure according to a preferred embodiment of the present invention includes a step of mounting an electronic component according to a preferred embodiment of the present invention or an electronic component produced by a production method according to a preferred embodiment of the present invention, on a land of a circuit board, and a step of firing the electronic component on the land, wherein the step of firing the electronic component is performed to sinter the metal particles included in the outermost layer of the outer electrode.

Preferred embodiments of the present invention provide electronic components that are each mountable on a circuit board without soldering or plating.

The above and other elements, features, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with reference to the attached drawings.

Hereinafter, electronic components, methods for producing electronic components, and methods for producing mount structures according to preferred embodiments of the present invention will be described with reference to the drawings.

However, the present invention is not limited to the following features, and changes may be appropriately made without departing from the spirit and scope of the present invention. Preferred embodiments in which two or more preferable features among the following features are combined also fall within the scope of the present invention.

Electronic Component

Electronic components according to preferred embodiments of the present invention are various chip electronic components. The electronic components are, for example, ceramic electronic components including a ceramic body. Examples of the ceramic electronic components include multilayer ceramic electronic components, such as multilayer ceramic capacitors, multilayer inductors, and multilayer LC components. Electronic components according to preferred embodiments of the present invention are not necessarily ceramic electronic components.

is a schematic sectional view illustrating an example of an electronic component according to a preferred embodiment of the present invention.

Referring to, an electronic componentincludes a body, an inner electrodedisposed within the body, and an outer electrodedisposed outside of the body. In the electronic component, the outer electrodeincludes, sequentially from outside to inside, an outermost layerand an underlying layer. The underlying layeris disposed on the surface of the body. The outermost layeris disposed on the surface of the underlying layer.

is a schematic sectional view illustrating another example of an electronic component according to a preferred embodiment of the present invention.

Referring to, an electronic componenthas the same or substantially the same configuration as in the electronic componentin, except that the outer electrodedoes not include the underlying layer, and the outermost layeris disposed on the surface of the body.

Such an electronic component according to a preferred embodiment of the present invention includes the following feature: an outer electrode includes an outermost layer that includes metal particles but is not electrically connected to an inner electrode.

As described below, an electronic component according to a preferred embodiment of the present invention is mountable on a circuit board without soldering or plating. Thus, a reduction in the quality described in (1) above is prevented. In particular, when the body is a ceramic body, a reduction in the quality of, in addition to (1) above, (2) and (3) is prevented.

is a schematic explanatory view of a method of checking electrical connection between an inner electrode and an outer electrode.

An electronic component is polished to expose a section. Referring to, an instrument is then attached to positions P, P, P, and P, and the four-point probe method is performed to measure the resistance between Pand P(about 2 cm to about 3 cm, for example). The voltage between Pand Pand the current between Pand Pare measured using, for example, a digital multimeter (PC7000, manufactured by SANWA ELECTRIC INSTRUMENT CO., LTD.).

When the measurement voltage is set to about 100 mV and electrical connection between the inner electrode and the outer electrode is not established, the current is less than about 1 mA or is unmeasurable. On the other hand, when electrical connection between the inner electrode and the outer electrode is established, a current of, for example, several tens of to several hundreds of milliamperes according to Ohm's law can be measured.

In an electronic component according to a preferred embodiment of the present invention, the metal particles included in the outermost layer of the outer electrode are not sintered. Stated another way, in the outermost layer of the outer electrode, necking between the metal particles does not occur. In the outermost layer of the outer electrode, the metal particles are dispersed within a resin described below. Thus, the outermost layer of the outer electrode is not electrically connected to the inner electrode.

The metal of the metal particles included in the outermost layer of the outer electrode is preferably, for example, Cu, Ni, Ag, or an alloy including at least one of these metals.

The metal particles included in the outermost layer of the outer electrode preferably have an average particle size of about 10 nm or more and about 1000 nm or less, for example. When the metal particles have an average particle size in this range, the metal particles can be sintered at a temperature lower than the melting point of the metal of the metal particles.

The average particle size of the metal particles included in the outermost layer of the outer electrode can be measured in the following manner. A scanning electron microscope (SEM) is used to observe, within a field of view of, for example, about 30 μm×about 30 μm, a section of the outermost layer of the outer electrode. The particle sizes of metal particles at 10 or more points are individually measured by the line method. The average particle size of the equivalent circular diameters of the metal particles within the field of view is defined as the average particle size of the metal particles.

The outermost layer of the outer electrode preferably has a thickness (inand, length denoted by arrow T) of about 1 μm or more, for example. In addition, the outermost layer of the outer electrode preferably has a thickness of, for example, about 100 μm or less.

The thickness of the outermost layer of the outer electrode can be measured in the following manner. A SEM is used to observe three random points in a section of the outermost layer of the outer electrode, such that the entire outermost layer (in the direction denoted by arrow T) of the outer electrode is within each field of view. In each field of view, the thickness of the outermost layer of the outer electrode is measured at three points. In all of the fields of view, this measurement is performed and the average value of the measured values at all of the measurement points is defined as the thickness of the outermost layer of the outer electrode.

The outermost layer of the outer electrode preferably further includes a thermally decomposable resin. The thermally decomposable resin may be of a single species or two or more species.

The thermally decomposable resin preferably has a thermal decomposition temperature of about 100° C. or more and about 350° C. or less, for example. The thermal decomposition temperature means, in measurement using a thermobalance at a heating rate of about 10° C./min, a temperature at which the weight of the resin decreases by about 5 wt %.

The thermally decomposable resin is preferably, for example, an acrylic resin, a butyral resin, or a cellulosic resin.

The acrylic resin is, for example, a homopolymer of an alkyl (meth)acrylate, or a copolymer including an alkyl (meth)acrylate as a main monomer (component accounting for about 50 mass % or more of the total monomer amount; hereafter, the same definition) and an auxiliary monomer that is copolymerizable with the main monomer. Specific examples of the homopolymer include polymethyl (meth)acrylate, polyethyl (meth)acrylate, and polybutyl (meth)acrylate. Specific examples of the copolymer include a block copolymer including, as constitutional units, a methacrylate polymer block and an acrylate polymer block. Incidentally, (meth)acrylate means acrylate and/or methacrylate.

The butyral resin is, for example, a homopolymer of vinyl acetate or a copolymer including vinyl acetate as a main monomer and an auxiliary monomer that is copolymerizable with the main monomer. Specific examples of the homopolymer include polyvinyl butyral. Specific examples of the copolymer include polyvinyl butyral (PVB) in which the main chain skeleton includes, as constitutional repeating units, vinyl butyral (butyral group), vinyl acetate (acetyl group), and vinyl alcohol (hydroxy group).

The cellulosic resin is, for example, a cellulose organic acid ester (cellulose derivative) in which the hydrogen atoms of the hydroxy groups of cellulose defining and functioning as a constitutional repeating unit are partially or entirely substituted with an alkyl group such as a methyl group, an ethyl group, a propyl group, an isopropyl group, or a butyl group, an acyl group such as an acetyl group, a propionyl group, or a butyryl group, a methylol group, an ethylol group, a carboxymethyl group, or a carboxyethyl group. Specific examples include methylcellulose, ethylcellulose, hydroxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, hydroxypropylmethylcellulose, carboxymethylcellulose, carboxyethylcellulose, carboxyethylmethylcellulose, cellulose acetate phthalate, and nitrocellulose.

The outermost layer of the outer electrode may further include a fixing auxiliary material, such as glass or a thermosetting resin, for example. This provides an increase in the fixing strength during mounting.

Examples of the glass included in the outermost layer of the outer electrode include glass including at least one selected from B, Si, Ba, Mg, Al, Li, P, Te, V, Bi, Sn, In, and Na. Examples of the thermosetting resin included in the outermost layer of the outer electrode include epoxy resins.

Referring to, when the outer electrode includes the underlying layer, the underlying layer is preferably a metallized layer, for example. The metallized layer includes glass and metal. Examples of the metal of the metallized layer include Cu, Ni, and Ag. The metallized layer is formed by applying an underlying-layer-forming conductive paste including glass and metal particles to the surface of the body and firing the conductive paste to achieve metallization. When the body is a ceramic body, the metallized layer may be formed by co-firing together with the ceramic body and the inner electrode, or may be formed by firing performed after firing of the ceramic body and the inner electrode.

The underlying layer preferably has a thickness of about 10 nm or more and about 100 μm or less, for example. The thickness of the underlying layer can be measured by the same method as in the thickness of the outermost layer. The underlying layer may include multiple layers.

In an electronic component according to a preferred embodiment of the present invention, the body, such as a ceramic body, is made of a material appropriately selected in accordance with the function of the electronic component. For example, when the electronic component is a ceramic capacitor, the body is made of a dielectric ceramic. Examples of the dielectric ceramic include perovskite compounds including Ba and Ti.

When the electronic component is a ceramic capacitor, the inner electrode is preferably made of, for example, a metal such as Ni, Cu, Ag, Pd, Au, or Ag—Pd alloy.

Method for Producing Electronic Component

Hereinafter, an example of a method for producing an electronic component according to a preferred embodiment of the present invention will be described.

is a schematic sectional view illustrating an example of a step of preparing a body within which an inner electrode is disposed.

A bodywithin which an inner electrodeis disposed is prepared. In a case of forming an underlying layerof the outer electrode as described later, the bodymay be a green body or a fired body.

is a schematic sectional view illustrating an example of a step of forming the underlying layer of the outer electrode.

On the surface of the body, the underlying layerof the outer electrode is formed. For example, an underlying-layer-forming conductive paste including glass and metal particles is applied to the surface of the bodyand fired, to thus form a metallized layer as the underlying layerof the outer electrode. As long as the underlying layeris electrically connected to the inner electrode, the material and formation process of the underlying layerare not particularly limited. For example, plating, sputtering, or vapor deposition may be performed to form the underlying layer.